-o option
Can be used to give options in the format used in the configura-
tion file. This is useful for specifying options for which there
is no separate command-line flag. For full details of the
options listed below, and their possible values, see
ssh_config(5).

StrictHostKeyChecking=no, again from the man page (last line)

ssh automatically maintains and checks a database containing identifica-
tion for all hosts it has ever been used with. Host keys are stored in
~/.ssh/known_hosts in the user's home directory. Additionally, the file
/usr/local/etc/ssh/ssh_known_hosts is automatically checked for known
hosts. Any new hosts are automatically added to the user's file. If a
host's identification ever changes, ssh warns about this and disables
password authentication to prevent server spoofing or man-in-the-middle
attacks, which could otherwise be used to circumvent the encryption. The
StrictHostKeyChecking option can be used to control logins to machines
whose host key is not known or has changed.

ec2-user@${STAGING_JUMP_IP:?} this bit is just using an env var with the jump ip address since all of the servers live in a(n) (AWS) VPC behind a proxy server (NGINX).
-L ${REMOTE_ADDRESS} -M -S ssh-socket -fN -4, cue the man page:

Specifies that connections to the given TCP port or Unix socket
on the local (client) host are to be forwarded to the given host
and port, or Unix socket, on the remote side. This works by
allocating a socket to listen to either a TCP port on the local
side, optionally bound to the specified bind_address, or to a
Unix socket. Whenever a connection is made to the local port or
socket, the connection is forwarded over the secure channel, and
a connection is made to either host port hostport, or the Unix
socket remote_socket, from the remote machine.
Port forwardings can also be specified in the configuration file.
Only the superuser can forward privileged ports. IPv6 addresses
can be specified by enclosing the address in square brackets.

this next function is just responsible for exiting the tunnel post deployment:

for all the ips specified as args to the script, tunnel, then, from the excellent CLI tldr:

$ tldr pushdpushd
Place a directory on a stack so it can be accessed later.
See also popd to switch back to original directory.
- Switch to directory and push it on the stack:
pushd directory
- Switch first and second directories on the stack:
pushd
- Rotate stack by making the 5th element the top of the stack:
pushd +4

where dist is where the build artefacts live, which then copy everything recursively using scp to the remote directory you want to your static files to live @, popd to remove a directory added to the dir stack via, you guessed it, pushd, and then call exit-staging-tunnel.